1. Field
The present invention relates generally to detonating cord, and more particularly to explosive assemblies formed from detonating cord, and further, to explosive assemblies forming a grid from detonating cord.
2. Description of the Problem and Related Art
The general concept of using detonating cord to make an explosive matrix as an explosive counter charge is well known, as exemplified by U.S. Pat. Nos. 2,455,354; 3,242,862; 4,768,417; 5,437,230; and 6,182,553; and by the U.S. Navy's Distributed Explosives Technology, described in “Distributed Explosive Technology (DET) Mine Clearance System (MCS) Ex 10 Mod 0 Program Life Cycle Cost Estimate for Milestone III” (Jun. 4, 1999). These prior designs were created for large military applications. Such applications require significant manpower and financial resources. These prior art explosive matrices must be manufactured well in advance of their usage. Field assembly is not practical because they are a complex of multiple lengths of detonating cords joined together. Moreover, due to cost, complexity and time of manufacturing, these prior art explosives matrices have been infeasible for commercial use as a blasting charge. In addition, these prior art explosive matrices are heavy and cumbersome to transport. They use rope or cord to hold the detonating cord together, creating undesirable bulk and weight.
Another shortcoming of these matrices results from the fact that detonating cord detonates linearly from the point of initiation, proceeding therefrom along the cord. Consequently, detonating cord can fail to propagate the detonation wave where the cord makes sharp turns, especially when large grain detonating cord is used. In some prior art designs, in order to assure sufficient transfer of the detonating wave between intersecting cords, clamps were used at all points of intersection of detonating cord. This adds further complexity and bulk to these prior art designs.
On the other hand, use of low grain non-propagating detonating cord is not always possible in prior art explosive matrices. Some prior art devices initiate at one point, in one direction, and use multiple lengths of detonating cord coupled together, which compromises reliability. To increase reliability, other explosive matrices incorporate multiple initiation points and multiple lengths of detonating cord, again making the design more complex and the assembly more complicated and expensive.
A later example that addressed many of these shortcomings is taught in U.S. Pat. No. 7,913,624 to the inventor hereof, wherein the explosive matrix assembly permits the construction of explosives counter charges which are more efficient, safer and less costly than the above mentioned prior art explosive matrices. It is typically assembled from a single length of detonating cord formed into a grid-like matrix pattern, and a small number of cable ties and or tape are required to force the detonating cord into 90 degree angles and to hold the assembly together. However, the detonating cord must be forced into position, which may be made easier with a field assembly tool, but the design of the field assembly tool sometimes creates less than perfect right angles throughout the matrix assembly. Furthermore, due to the geometric design of the grid, the matrix will always have intersections that consist of four over-laid sections of detonating cord, while two of the outer sides will always have three over-laid sections of detonating cord. This makes the charge non-uniform.